Video was posted on Twitter by a user named Danny Rockett following the Cubs' 5-1 loss to the Pittsburgh Pirates.
It shows fans throwing punches as those around them try to break up the fighting before security steps in.
One peacemaker can be seen shouting, "There's no fighting in the bleachers!"
Rockett tweeted, "Dudes were racist. Didn't see the first punch. But I saw the 3rd-56th."
When asked what started the fight, Rockett replied, "Racism."